Systems for a multi-fuel capable engine

ABSTRACT

Various methods and systems are provided for a multi-fuel capable engine. The system includes a liquid fuel system to deliver liquid fuel to an engine, a gaseous fuel system to deliver gaseous fuel to the engine, and a control system. The control system, during a gaseous fuel system test mode, controls the liquid fuel system and the gaseous fuel system to deliver the liquid fuel and the gaseous fuel to the engine over a range of engine operating points, and indicate degradation of the gaseous fuel system based on engine output at each of the engine operating points.

FIELD

Embodiments of the subject matter disclosed herein relate to multi-fuelcapable engine systems.

BACKGROUND

Some stationary power plants and some vehicles may include an enginethat is powered by one or more fuel sources to generate mechanicalenergy. Mechanical energy may be converted to electrical energy that isused to power traction motors and other components and systems of thevehicle. During use, some of the engine parts might wear, warp, ordegrade. This may affect their performance over time. It may bedesirable to have a system that accounts for such changes over time tomaintain or improve performance.

BRIEF DESCRIPTION

In one embodiment, a system comprises a liquid fuel system to deliverliquid fuel to an engine, a gaseous fuel system to deliver gaseous fuelto the engine, and a control system. The control system is configuredto, during a gaseous fuel system test mode, control the liquid fuelsystem and the gaseous fuel system to deliver the liquid fuel and thegaseous fuel to the engine over a range of engine operating points, andindicate degradation of the gaseous fuel system based on engine outputat each of the engine operating points.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 shows a schematic diagram of two locomotives, a fuel tender, anda freight car according to an embodiment of the invention.

FIG. 2 shows a schematic diagram of an example fuel tender and naturalgas-fueled locomotive according to an embodiment of the invention.

FIG. 3 shows a schematic diagram of a cylinder of a multi-fuel engineaccording to an embodiment of the invention.

FIG. 4 shows a schematic diagram of a multi-fuel engine according to anembodiment of the invention.

FIG. 5 is a high-level flow chart for operating a multi-fuel engine inone or more selected modes according to an embodiment of the invention.

FIG. 6 is a flow chart illustrating a method for operating a multi-fuelengine according to an embodiment of the invention.

FIG. 7 is a flow chart illustrating a method for operating a multi-fuelengine in a gaseous fuel system performance test mode according to anembodiment of the invention.

FIG. 8 is a flow chart illustrating a method for operating a multi-fuelengine in a gaseous fuel system leak test mode according to anembodiment of the invention.

FIG. 9 is a flow chart illustrating a method for operating a multi-fuelengine in a gaseous fuel vent mode according to an embodiment of theinvention.

DETAILED DESCRIPTION

The following description relates to various embodiments of methods andsystems for a multi-fuel capable engine. In one example, the multi-fuelcapable engine receives liquid fuel from a liquid fuel system andreceives gaseous fuel from a gaseous fuel system. The liquid fuel maycomprise one or more of gasoline, diesel, ethanol, or other fuel type.The gaseous fuel may comprise one or more of compressed natural gas,liquefied natural gas, hydrogen, or other fuel type. The multi-fuelcapable engine may be installed in a vehicle, such as a rail vehicle, ina stationary platform, in a marine vessel, or other suitable system. Themulti-fuel capable engine may be controlled via a control system. Forexample, the control system may be configured to, during a gaseous fuelsystem test mode, control the liquid fuel system and the gaseous fuelsystem to deliver the liquid fuel and the gaseous fuel to the engineover a range of engine operating points, and indicate degradation of thegaseous fuel system based on engine output at each of the engineoperating points.

An example of a platform supporting a multi-fuel capable engine isillustrated in FIGS. 1-2. Additional details of the multi-fuel capableengine are illustrated in FIGS. 3-4. As explained above, the multi-fuelcapable engine combusts liquid fuel, such as diesel, as well as gaseousfuel, such as natural gas, during certain operating modes, asillustrated in FIGS. 5-6. To ensure the gaseous fuel system is operatingas desired, for example to ensure the gaseous fuel system is sendinggaseous fuel at a commanded rate, a gaseous fuel system performance testmay be carried out, as illustrated in FIG. 7. Further, to preventleakage of the gaseous fuel to atmosphere, a gaseous fuel system leaktest may be performed, as illustrated in FIG. 8, and/or excess gaseousfuel in the gaseous fuel system supply lines may be vented through theengine and exhaust system prior to engine shutdown, as illustrated inFIG. 9. In doing so, desired performance of the gaseous fuel system maybe ensured while minimizing emissions.

The approach described herein may be employed in a variety of enginetypes, and a variety of engine-driven systems. Some of these systems maybe stationary, while others may be on semi-mobile or mobile platforms.Semi-mobile platforms may be relocated between operational periods, suchas mounted on flatbed trailers. Mobile platforms include self-propelledvehicles. Such vehicles can include on-road transportation vehicles, aswell as mining equipment, marine vessels, rail vehicles, and otheroff-highway vehicles (OHV). For clarity of illustration, a locomotive isprovided as an example of a mobile platform supporting a systemincorporating an embodiment of the invention.

With reference to FIG. 1, a schematic diagram illustrates a consist ofvehicles. This consist includes a first locomotive 100, a secondlocomotive 104, a tender 110, and a freight car 108. The tender is afuel tank that may carry one or more fuel for supply to one or morecoupled locomotive. Specifically, FIG. 1 shows the first locomotiveremovably coupled to the second locomotive and removably coupled to thefuel tender. The fuel tender is shown removably coupled to the freightcar. Additional fuel tenders, freight cars, locomotives, and/or otherrailroad vehicles may be removably connected to the freight car and/orthe second locomotive. The order of the various railroad vehicles shownin FIG. 1 may be modified. For example, FIG. 1 shows the secondlocomotive as the lead vehicle of the consist and the freight car as thetrail vehicle. However, in other embodiments the first locomotive may bethe trail vehicle. In one embodiment, the first locomotive may be thelead vehicle with the tender coupled between the first locomotive andthe second locomotive. In this example, the fuel tender provides naturalgas fuel, in this case compressed natural gas (CNG) to both the firstlocomotive and the second locomotive. In some embodiments, the tendermay send CNG directly to the first locomotive through a first fluidiccoupling and send CNG directly to the second locomotive through a secondfluidic coupling.

The first locomotive, the second locomotive, the tender, and the freightcar are configured to run on a rail 102 (or set of rails) via aplurality of wheels. In FIG. 1, the tender is positioned behind thefirst locomotive and removably coupled to the freight car. In otherconfigurations, the tender may be positioned in front of the locomotiveand/or may not be connected to the freight car or other rail car. Instill other configurations, one or more other rail cars may be locatedbetween the tender and the first locomotive. In another configuration,the tender may be located between the first locomotive and the secondlocomotive.

In one example the first locomotive and second locomotive are poweredfor propulsion, while the tender and freight car are non-powered. Itwill be appreciated that in other examples one or more of the tender andfreight car may also be powered for propulsion by, for example, one ormore traction motors.

Additionally, FIG. 1 shows a tender controller 220 on board the tender,a first locomotive controller 136 on board the first locomotive, and asecond locomotive controller 194 on board the second locomotive. Asdescribed further below, the first locomotive controller controlsoperation of a primary engine 118 and the tender controller controlsoperation of the tender. However, the first locomotive controller maysend signals and/or requests (e.g., commands) to the tender controllerregarding operation of the tender. For example, the first locomotivecontroller may send a request to the tender controller of the tender toconvert liquid natural gas to gaseous natural gas and send the gaseousnatural gas via one or more fuel lines to an engine of the firstlocomotive, as described further below. Further, the first locomotivecontroller may include instructions stored thereon (e.g., within amemory of the controller) for sending a plurality of requests to thetender controller and to components on board the tender. The tendercontroller may then control actuators and/or components on board thetender based on the requests sent from the first locomotive controlleron board the first locomotive. As shown in FIG. 1, the tendercontroller, first locomotive controller, and second locomotivecontroller all communicate electronically with one another.

Turning now to FIG. 2, the first locomotive includes an engine system112 that comprises an engine 118 having a plurality of cylinders. Theengine may be referred to herein as the locomotive engine. In oneembodiment, each cylinder has at least one gaseous admission valve toadmit gaseous fuel to the cylinder and at least one liquid fuel injectorto inject liquid fuel to the cylinder. However, other configurations arepossible, such as single-point gaseous fuel fumigation system where thegaseous fuel is mixed with the intake air upstream of the cylinders(e.g., in an intake manifold or intake passage) rather than supplied toeach cylinder individually. In an example, the first locomotive has anengine system that operates on plural fuel types, such as a first fueland a second fuel. The fuel types may include a liquid fuel and agaseous fuel. Suitable liquid fuels may include diesel fuel, whilesuitable gaseous fuel may include natural gas. The engine is amulti-fuel capable engine. Examples of suitable multi-fuel capableengines may include a gas turbine, compression ignition engine, or sparkignition engine. A gaseous fuel may be natural gas that is received fromthe tender via a compressed natural gas (CNG) fluidic coupling 114(e.g., fuel line), and a second fuel may be diesel fuel received from adiesel storage tank 116 via a liquid fuel fluidic coupling 122 on boardthe first locomotive. Other examples of engine systems may use variouscombinations of fuels other than diesel and natural gas, such as ethanoland hydrogen. In an example, gaseous fuel from the tender (e.g., naturalgas) is supplied to the cylinders to form a gaseous fuel/air mixturethat is combusted due to compression ignition of the injected liquidfuel (e.g., diesel fuel). The relative ratio of gaseous fuel to liquidfuel as well as injection timing of the liquid fuel may be adjustedbased on various operating parameters.

The engine generates torque that is transmitted to a power conversionunit 120 along a drive shaft 124. The power conversion unit isconfigured to convert the torque into electrical energy that isdelivered via a first electrical bus 128 to at least one traction motor132 and to a variety of downstream electrical components in the firstlocomotive. Such components may include, but are not limited to,compressors 140, blowers 144, batteries 148, an electronics controlsystem 134 including one or more controllers, shutoff valves, pressureregulators, radiators, lights, on-board monitoring systems, displays,climate controls (not shown), and the like. The first electrical bus maydeliver electrical energy to the tender.

Based on the nature of the generated electrical output, the firstelectrical bus may be a direct current (DC) bus (as depicted) or analternating current (AC) bus. In one example the power conversion unitincludes an alternator (not shown) that is connected in series to one ormore rectifiers (not shown) that convert the alternator's electricaloutput to DC electrical power prior to transmission along the firstelectrical bus. The alternator may include, for example, a high-speedgenerator, a generator machine whose stator flux is synchronous to therotor flux, or an asynchronous machine.

Based on the configuration of a downstream electrical componentreceiving power from the first electrical bus, one or more inverters maybe configured to invert the electrical power from the first electricalbus prior to supplying electrical power to the downstream component. Inone example, a single inverter may supply AC electrical power from a DCelectrical bus to a plurality of components. In another non-limitingembodiment, each of a plurality of distinct inverters may supplyelectrical power to a distinct component.

The traction motor receives electrical power from the power conversionunit and is coupled to one or more axles/driving wheels 152. In thismanner, the traction motor is configured to drive the axles/drivingwheels along the rail. It should be appreciated that the number of setsof axles/driving wheels may vary, and that one or more traction motorsmay be provided for each set of axles/driving wheels. The traction motormay be an AC motor. Accordingly, an inverter paired with the tractionmotor may convert DC input to an appropriate AC input, such as athree-phase AC input, for subsequent use by the traction motor. In othernon-limiting embodiments, the traction motor may be a DC motor directlyemploying the output of the power conversion unit after rectificationand transmission along the DC electrical bus.

One example locomotive configuration includes one inverter/tractionmotor pair per axle/driving wheel. The traction motor may also beconfigured to act as a generator providing dynamic braking to brake thefirst locomotive. In particular, during dynamic braking, the tractionmotor may provide torque in a direction that is opposite from therolling direction, thereby generating electricity that is dissipated asheat by a power dissipation unit (e.g., set of resistors) 180 connectedto the first electrical bus. The set of resistors (also referred to as aresistive grid) may be configured to dissipate excess engine torque viaheat produced by the grids from electricity generated by the powerconversion unit.

The first locomotive controller on board the first locomotive controlsthe engine by sending commands to various engine control hardwarecomponents such as invertors, alternators, relays, fuel injectors, gasadmission valves, fuel pumps (not shown), or the like. As describedfurther below, in one example, the first locomotive controller alsomonitors locomotive operating parameters in active operation, idle, andshutdown states. Such parameters may include, but are not limited to,manifold air temperature (MAT), ambient temperature, engine oiltemperature, compressor air pressure, main air reserve pressure, batteryvoltage, a battery state of charge, brake cylinder pressure, or thelike. The first locomotive controller further includes computer readablestorage media (not shown) including code for enabling on-boardmonitoring and control of rail vehicle operation.

The first locomotive controller, while overseeing control and managementof the engine and other locomotive components, may be configured toreceive signals from a variety of engine sensors, as further describedherein. The first locomotive controller may utilize such signals todetermine operating parameters and operating conditions, andcorrespondingly adjust various engine actuators to control operation ofthe first locomotive. For example, the first locomotive controller mayreceive signals from various engine sensors including, but not limitedto, engine speed, engine load, boost pressure, exhaust pressure, ambientpressure, exhaust temperature, manifold pressure (MAP), or the like.Correspondingly, the first locomotive controller may control the firstlocomotive by sending commands to various components such as tractionmotors, alternators, cylinder valves, throttles, or the like. Asdescribed further below, the first locomotive controller at leastpartially controls operation of the fuel tender by sending commands(e.g., requests) to the tender controller on board the fuel tender. Forexample, the commands sent to the tender controller may include commandsfor controlling various components on board the fuel tender such as avaporizer 234, a pump 210, a LNG storage tank 212, or the like. Inanother example, the commands sent to the tender controller may includerequests for CNG (e.g., a request to send CNG to the first locomotive).Then, in response to the request for CNG, the tender controller mayadjust one or more of the vaporizer, the pump, and/or one or more valvescontrolling flow of LNG and/or CNG in order to deliver the requested CNGto the first locomotive.

In some embodiments, the vaporizer may be referred to as aregasification unit. For purposes of this description, an “on-board”component, device, or other structure means that the component or deviceis physically located on the vehicle being described. For example, withrespect to the tender, a component or structure physically located onthe fuel tender is on board the fuel tender, including when the fueltender is coupled to a locomotive or other rail vehicle and when thefuel tender is not coupled to a locomotive or other rail vehicle.

In one embodiment, the computer readable storage media configured in thefirst locomotive controller may execute code to auto-stop or auto-startthe engine by enabling, for example, an Automatic Engine Start/Stop(AESS) control system routine. As discussed in more detail below, thefirst locomotive controller also communicates with the tender controlleron board the tender to, for example, request delivery of gaseous naturalgas for the engine. As shown in FIGS. 1-2, the first locomotivecontroller also communicates with the second locomotive controller inthe second locomotive to, for example, coordinate pass-through deliveryof gaseous natural gas from the tender to a natural-gas fueled engine inthe second locomotive. The computer readable storage media configured inthe first locomotive controller may execute code to appropriatelytransmit and receive such communications.

With continued reference to FIG. 2, the tender is removably coupled tothe first locomotive and includes axles/wheels 204 configured to travelalong the rail. In the depicted example, the tender includes six pairsof axles/wheels. In another example, the tender includes four pairs ofaxles/wheels. The tender further includes a mechanical couplingmechanism 208 that removably couples the fuel tender to the firstlocomotive for linked movement thereof. In other examples, the tendermay include a second coupling mechanism (not shown) that may removablycouple the fuel tender to another rail vehicle, such as the freight caror an additional locomotive (e.g., such as the second locomotive).

The tender is configured to carry one or more fuel storage tanks. In oneembodiment, as shown in FIG. 2, the tender includes an on-boardcryogenic LNG storage tank for storing LNG. The LNG storage tank is afuel container wherein the fuel stored in the fuel container is LNG. Inone example, the LNG storage tank may take the form of a vacuum jacketedpressure vessel that stores LNG at pressures ranging from approximately10 psi to approximately 130 psi. It will be appreciated that to maintainLNG in a liquid state, the LNG may be stored at a temperature range ofapproximately 4-80 degrees Celsius. In another example, the LNG may bestored at a temperature above or below the range of 4-80 degreesCelsius. In yet another example, the LNG may be stored at a temperaturerange of approximately 60-120 degree Celsius. In some examples, as shownin FIG. 2, the tender includes a cryogenic unit 268 for helping maintainthe LNG within desired temperature and pressure ranges. In otherexample, the tender may not include the cryogenic unit. Even withefficient insulation and cryogenic refrigeration equipment, heat mayleak into the LNG storage tank and causes vaporization of portions ofthe LNG into boil-off gas.

It will also be appreciated that the LNG storage tank may have varioussizes and configurations and may be removable from the tender. Further,as shown in FIG. 2, the storage tank is configured to receive LNG froman external refueling station via port 222. In alternate examples, thestorage tank may revive LNG through another port or location on thestorage tank.

The LNG storage tank supplies LNG via cryogenic LNG fluidic coupling 226and one or more valves 230 to the vaporizer. The vaporizer converts theLNG into gaseous or compressed natural gas (CNG), or vaporizes the LNG,by the application of heat to the LNG. Specifically, the vaporizervaporizes the LNG to CNG by utilizing heated fluid supplied to thevaporizer. As shown in in FIG. 2, heated fluid for the conversion of LNGto CNG is generated by a heat exchanger 170 positioned on the firstlocomotive. The heat exchanger receives engine cooling water from aradiator 172. Engine cooling water from the engine flows to the radiatorto be cooled and then sent back to the engine. Before the cooled enginecooling water flows back to the engine, the cooled engine cooling waterpasses through the heat exchanger to heat a secondary fluid, or coolant.The coolant heated at the heat exchanger then flows from the heatexchanger to the vaporizer on the tender via a first heated coolant line174 and a second heated coolant line 274. The first heated coolant lineand the second heated coolant line are coupled together at a detachableinterface coupling 276 that enables the tender to be decoupled from thefirst locomotive. Coolant then returns to the heat exchanger via a firstcoolant line 278 and a second coolant line 178. The first coolant lineand the second coolant line are coupled together at a detachableinterface coupling 280 that enables the tender to be decoupled from thefirst locomotive. In alternate embodiments, heat may be supplied to thevaporizer from an alternative source on board the first locomotive,another locomotive, and/or fuel tender. Further, additional and/oralternative liquid or gas sources may be used to provide heat to thevaporizer.

The CNG is then delivered to the engine of the first locomotive to powerthe engine. As shown in FIG. 2, the CNG is delivered to the engine viaCNG fluidic coupling 216 and CNG fluidic coupling and one or morecontrol valves 232. In some examples, as shown in FIG. 2, a pass-throughcontrol valve 156 is provided to direct at least a portion of the CNGthrough the first locomotive via a pass through fluidic coupling 160 tothe second locomotive. In this manner, a natural gas-fueled engine inthe second locomotive may be powered by gaseous natural gas from thetender. In alternate examples, there may not be a control valve and CNGmay only be delivered to the first locomotive. In yet another example,additional control valves may be positioned in the CNG fluidic couplingto direct CNG to additional locomotives or rail cars. In some examples,additional control valves may be positioned in the CNG fluidic couplingto direct CNG to additional locomotives or rail cars. For example, in anembodiment wherein the tender is positioned between the first locomotiveand the second locomotive, the tender may send CNG to the firstlocomotive and the second locomotive through separate fluidic couplings.As such, the second locomotive may receive CNG directly from the tenderand not through another locomotive.

In a first embodiment, the LNG storage tank may be a higher pressure LNGstorage tank wherein the LNG is maintained at a pressure greater than athreshold supply pressure. In one example, the threshold supply pressureof CNG may be approximately 120 psi. The pressure within the LNG storagetank may then be maintained above 120 psi (e.g., 160 psi) so the CNGarriving at the first locomotive is at the threshold supply pressure. Inother examples, the threshold supply pressure of CNG may be greater orless than 120 psi and the LNG storage tank pressure may be maintained ata level greater than the threshold supply pressure to account for anypressure losses in the CNG supply system. In this first embodiment, LNGis metered from the LNG storage tank and to the vaporizer by the valve230, or other metering device. CNG converted from the LNG at thevaporizer then flows to the first locomotive via the CNG fluidiccoupling. The flow of CNG to the first locomotive is controlled ormetered via the valve 232.

In a second embodiment, the LNG storage tank may be a lower pressure LNGstorage tank wherein the LNG is maintained at a pressure lower than thethreshold supply pressure (e.g., less than 120 psi). For example, theLNG storage tank may maintain the LNG at a lower pressure of 50 psi. Inthis embodiment, the pump may be positioned in the LNG fluidic couplingto control a flow (e.g., flow rate) of LNG to the vaporizer and/or inthe CNG fluidic coupling to control a flow (e.g., flow rate) of CNG tothe first locomotive. In alternate embodiments, the pump may bepositioned additionally or alternatively on the first locomotive.

The CNG fluidic coupling further includes a detachable interfacecoupling 236 that enables the tender to be decoupled from thelocomotive. It will also be appreciated that in other embodiments thepass-through control valve may be located on board the tender, alongwith suitable fluidic couplings to pass through the fluidic coupling.

It will be appreciated that by converting the LNG to CNG on board thetender and supplying CNG to the engine, standard gaseous natural gasconduit and interface couplings may be utilized between the fuel tenderand the locomotive. Advantageously, such a configuration avoids costlycryogenic tubing and interface couplings, and the corresponding designchallenges, that would otherwise be required for transferring LNGbetween the tender and the locomotive. Additionally, using suchstandard, low pressure gaseous natural gas fluidic and interfacecouplings eliminates the possibility of LNG leaks between the tender andlocomotive.

Components on the tender are powered with electrical energy from thefirst locomotive. Specifically, the first electrical bus is coupled to asecond electrical bus 228 at a detachable interface coupling 214. Thedetachable interface coupling enables the tender to be decoupled fromthe first locomotive. The first electrical bus and the second electricalbus may be referred to herein as electrical energy lines. In oneembodiment, the rail vehicle may include one or more electrical energylines traversing a space between the first locomotive and the tender.

Electrical energy generated at the first locomotive travels to thetender through the second electrical bus. Components on board the tenderreceive electrical energy via the second electrical bus. Such componentsmay include, but are not limited to, the vaporizer, tender controller,control valves 230, 232, LNG tank pressure sensor 260, LNG tanktemperature sensor 264, the cryogenic unit, flow meters, ambient airtemperature sensors, compressors, blowers, radiators, batteries, lights,on-board monitoring systems, displays, climate controls (not shown), andthe like.

The tender controller on board the tender controls and/or actuatesvarious components on board the tender, such as the vaporizer, thecryogenic unit, control valves (e.g., valve 230 and valve 232), one ormore pumps, and/or other components on board the tender, by sendingcommands to such components. The commands sent by the tender controllermay be based on commands sent to the tender controller from the firstlocomotive controller on board the first locomotive. For example, thefirst locomotive controller may send a request to the tender controllerto stop vaporizing LNG and thereby stopping the conversion of LNG toCNG. In response, the tender controller may actuate the vaporizer toturn off or stop vaporizing LNG.

The tender controller may also monitor fuel tender operating parameters.Such parameters may include, but are not limited to, pressure andtemperature of the LNG storage tank, a level or volume of the LNGstorage tank, pressure and temperature of the vaporizer, ambient airtemperature, and the like. In one example, the tender controller maysend a fuel value measurement measured at the LNG storage tank to thefirst locomotive controller on board the first locomotive.

It will be appreciated that the tender is not limited to the componentsshown in the example of FIG. 2 and described above. In other examples,the tender may include additional or alternative components. As anexample, the tender may further include one or more additional sensors,flow meters, control valves, or the like.

Locomotive may include a throttle 142 coupled to the engine to indicatepower levels. In this embodiment, the throttle is depicted as a notchthrottle. Additionally, a suitable throttle position may be one selectedfrom an infinitely variable setting level. Each notch of the notchthrottle may correspond to a discrete power level, that is, the notchthrottle may be a set of discrete, pre-determined power levels. Thesenotch settings may correspond to efficient operating speeds or powerlevels for the engine, and may further take into account additionalfactors (such as emissions levels, vibration harmonics, and the like).The power level indicates an amount of load, or engine output, placed onthe locomotive and controls the speed at which the locomotive willtravel. Although eight notch settings are depicted in the exampleembodiment of FIG. 2, in other embodiments, the throttle notch may havemore than eight notches or less than eight notches, as well as notchesfor idle and for dynamic brake modes. In some embodiments, the notchsetting may be selected by a human operator of the locomotive. In otherembodiments, the controller may determine a trip plan including notchsettings based on engine and/or locomotive operating conditions.

FIG. 3 depicts an embodiment of a combustion chamber, or cylinder 300,of a multi-cylinder internal combustion engine, such as the engine onboard the locomotive described above with reference to FIG. 1. Thecylinder may be defined by a cylinder head 301, housing the intake andexhaust valves and liquid fuel injector, described below, and a cylinderblock 303.

The engine may be controlled at least partially by a control systemincluding controller which may be in further communication with avehicle system, such as the locomotive described above with reference toFIG. 1. As described above, the controller may further receive signalsfrom various engine sensors including, but not limited to, engine speed,engine load, boost pressure, exhaust pressure, ambient pressure, CO₂levels, exhaust temperature, NO_(x) emission, engine coolant temperature(ECT) from temperature sensor 330 coupled to cooling sleeve 328, etc.Correspondingly, the controller may control the vehicle system bysending commands to various components such as alternator, cylindervalves, throttle, fuel injectors, etc.

The cylinder (i.e., combustion chamber) may include cylinder liner 304with a piston 306 positioned therein. The piston may be coupled to acrankshaft 308 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. In some embodiments, theengine may be a four-stroke engine in which each of the cylinders firesin a firing order during two revolutions of the crankshaft. In otherembodiments, the engine may be a two-stroke engine in which each of thecylinders fires in a firing order during one revolution of thecrankshaft.

The cylinder receives intake air for combustion from an intake includingan intake passage 310. The intake passage receives intake air via anintake manifold. The intake passage may communicate with other cylindersof the engine in addition to the cylinder 300, for example, or theintake passage may communicate exclusively with the cylinder 300.

Exhaust gas resulting from combustion in the engine is supplied to anexhaust including an exhaust passage 312. Exhaust gas flows through theexhaust passage, to a turbocharger in some embodiments (not shown inFIG. 3) and to atmosphere, via an exhaust manifold. The exhaust passagemay further receive exhaust gases from other cylinders of the engine inaddition to the cylinder 300, for example.

Each cylinder of the engine may include one or more intake valves andone or more exhaust valves. For example, the cylinder is shown includingat least one intake poppet valve 314 and at least one exhaust poppetvalve 316 located in an upper region of cylinder. In some embodiments,each cylinder of the engine, including the cylinder, may include atleast two intake poppet valves and at least two exhaust poppet valveslocated at the cylinder head.

The intake valve may be controlled by the controller via an actuator318. Similarly, the exhaust valve may be controlled by the controllervia an actuator 320. During some conditions, the controller may vary thesignals provided to the actuators to control the opening and closing ofthe respective intake and exhaust valves. The position of the intakevalve and the exhaust valve may be determined by respective valveposition sensors 322 and 324, respectively, and/or by cam positionsensors. The valve actuators may be of the electric valve actuation typeor cam actuation type, or a combination thereof, for example.

The intake and exhaust valve timing may be controlled concurrently orany of a possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. In other embodiments, the intake and exhaust valves may becontrolled by a common valve actuator or actuation system, or a variablevalve timing actuator or actuation system. Further, the intake andexhaust valves may by controlled to have variable lift by the controllerbased on operating conditions.

In still further embodiments, a mechanical cam lobe may be used to openand close the intake and exhaust valves. Additionally, while afour-stroke engine is described above, in some embodiments a two-strokeengine may be used, where the intake valves are dispensed with and portsin the cylinder wall are present to allow intake air to enter thecylinder as the piston moves to open the ports. This can also extend tothe exhaust, although in some examples exhaust valves may be used.

In some embodiments, each cylinder of the engine may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, FIG. 3 shows the cylinder including a fuel injector 326. Thefuel injector is shown coupled directly to the cylinder for injectingfuel directly therein. In this manner, the fuel injector provides whatis known as direct injection of a fuel into the combustion cylinder. Thefuel may be delivered to the fuel injector from a first, liquid fuelsystem 332, including a fuel tank, fuel pumps, and a fuel rail(described in more detail with respect to FIG. 4). In one example, thefuel is diesel fuel that is combusted in the engine through compressionignition. In other non-limiting embodiments, the fuel may be gasoline,kerosene, biodiesel, or other petroleum distillates of similar densitythrough compression ignition (and/or spark ignition).

Further, each cylinder of the engine may be configured to receivegaseous fuel (e.g., natural gas) alternative to or in addition to dieselfuel. The gaseous fuel may be provided to the cylinder via the intakemanifold, as explained below. As shown in FIG. 3, the intake passage mayreceive a supply of gaseous fuel from a second, gaseous fuel system 334,via one or more gaseous fuel lines, pumps, pressure regulators, etc.,located upstream of the cylinder. In some embodiments, the gaseous fuelsystem may be located remotely from the engine, such as on a differentrail car (e.g., on a fuel tender car), and the gaseous fuel may besupplied to the engine via one or more fuel lines that traverse theseparate cars. However, in other embodiments the gaseous fuel system maybe located on the same rail car as the engine.

A plurality of gas admission valves, such as gas admission valve 336,may be configured to supply gaseous fuel from the gaseous fuel system toeach respective cylinder via respective intake passages. For example, adegree and/or duration of opening of the gas admission valve may beadjusted to regulate an amount of gaseous fuel provided to the cylinder.As such, each respective cylinder may be provided with gaseous fuel froman individual gas admission valve, allowing for individual cylindercontrol in the amount of gaseous fuel provided to the cylinders.However, in some embodiments, a single-point fumigation system may beused, where gaseous fuel is mixed with intake air at a single pointupstream of the cylinders. In such a configuration, each cylinder may beprovided with substantially similar amounts of gaseous fuel. To regulatethe amount of gaseous fuel provided by the single-point fumigationsystem, in some examples a gaseous fuel control valve may be positionedat a junction between a gaseous fuel supply line and the engine intakeair supply line or intake manifold. The gaseous fuel control valvedegree and/or duration of opening may be adjusted to regulate the amountof gaseous fuel admitted to the cylinders. In other examples, the amountof gaseous fuel admitted to the cylinders in the single-point fumigationsystem may be regulated by another mechanism, such as control of agaseous fuel regulator, via control of a gaseous fuel pump, etc.

FIG. 4 illustrates multiple cylinders of engine 118, including cylinder300, cylinder 402, cylinder 404, and cylinder 406. While four cylindersarranged in-line are illustrated in FIG. 4, such an arrangement isnon-limiting, and other engine configurations are possible. For example,the engine may be a V-6, V-8, V-12, V-16, I-6, I-8, or other enginetype. The engine may be supplied one or more of liquid fuel from theliquid fuel system and gaseous fuel from the gaseous fuel system. Assuch, each cylinder of the engine includes a liquid fuel injector,including injector 326 as well as injectors 408, 410, and 412. Eachliquid fuel injector is supplied with liquid fuel from a common fuelrail 414. The common fuel rail may be supplied with fuel from a liquidfuel tank (e.g., the diesel fuel storage tank) via the liquid fuelfluidic coupling. The fuel may be provided at a high pressure via one ormore fuel pumps, such as pump 418. The liquid fuel in the liquid fuelsystem may be diesel fuel or another liquid fuel, such as gasoline,alcohol, etc. Further, while a common fuel rail system is illustrated inFIG. 4, a non-common rail unit pump injection system may be used.

Each cylinder of engine may similarly include a gas admission valve tosupply gaseous fuel, including gas admission valve 336 as well as gasadmission valves 422, 424, and 426. Each gas admission valve may bepositioned in an intake passage of a respective cylinder, or othersuitable location. The gas admission valves may be supplied gaseousfuel, such as natural gas, from a gaseous fuel passage 428. The gaseousfuel passage may receive gaseous fuel from a gaseous fuel tank (such asthe LNG storage tank 212) via a gaseous fuel supply line, such as theCNG fluidic coupling. As explained previously, the LNG storage tank maybe located remotely from engine, such as on board the tender, and maysupply fuel to the CNG fluidic coupling via the CNG fluidic coupling.However, in some embodiments, the individual gas admission valves may bedispensed with, and all the cylinders may be supplied with the samegaseous fuel/intake air mixture from an upstream single-point fumigationsystem.

In some examples, an air purge line 434 may be fluidically coupled toCNG fluidic coupling in order to route fresh air (via an air filter, forexample) through the gaseous fuel supply lines. Additionally, a gaseousfuel vent line 436 may route gaseous fuel to atmosphere during someconditions, explained in further detail below with respect to FIG. 9.Further still, a pressure regulator 438 may be positioned in the CNGfluidic coupling and configured to control the pressure of the gaseousfuel supplied to the engine.

The flow of gaseous fuel and/or air through the gaseous fuel system maybe controlled by one or more gaseous fuel valves. As explainedpreviously, a control valve 232 may be present on board the tender tocontrol passage of gaseous fuel from the vaporizer to the locomotive.Other gaseous fuel valves may be present on board the locomotive,including an air purge valve 440 positioned in the air purge line, afirst gaseous fuel valve positioned in the CNG fluidic coupling upstreamof the pressure regulator, a second gaseous fuel valve 444 coupledacross the pressure regulator in a bypass passage, a third gaseous fuelvalve 446 positioned in CNG fluidic coupling downstream of the pressureregulator, and a vent valve 448 positioned in the gaseous fuel ventline. Each of the gaseous fuel valves as wells the vent and purge valveson board the locomotive described above may be controlled by controller.However, in some embodiments one or more of the valves may be apressure-sensitive valve that opens and closes based on a pressureacross the valve, and not based on a command from the controller.Further, other manually controlled valves (e.g., check valves) notillustrated may be present in the gaseous fuel system.

Each liquid fuel injector of each cylinder, as well as each gasadmission valve of each cylinder, may be individually controlled by acontroller (such as controller) to enable individual cylinder control ofthe fuel supply. Accordingly, each cylinder may be operated with varyinglevels of liquid fuel and/or gaseous fuel. In some embodiments, theliquid fuel injectors may be controlled by a different controller thanthe controller that controls the gas admission valves. Further, in agaseous fumigation system, rather than controlling the individual gasadmission valves, a single gaseous fuel control valve or other gaseousfuel control element may be controlled by the controller to regulate theamount of gaseous fuel admitted to the cylinders.

In an example, a mixture of gaseous fuel and air may be provided tocylinder 300 via the intake passage and, in some embodiments, the gasadmission valve. Then, during compression, diesel fuel may be injectedto cylinder 300 via fuel injector 326. The diesel fuel may be ignitedvia compression ignition and subsequently ignite the gaseous fuel.Similar combustion events may occur for each cylinder of engine.

Thus, the systems described above with respect to FIGS. 1-4 provide fora multi-cylinder engine adapted to combust liquid fuel, and in somemodes of operation, both liquid and gaseous fuel according to variouscontrol methods stored on and configured to be executed by a controlsystem (including the controller). As further explained below withrespect to FIGS. 5-9, these control methods may include the locomotiveoperating with liquid and/or gaseous fuel combustion in a self-load modeor in conventional propulsion mode. Further, the control methods mayspecify that the locomotive operate under various test modes in order todiagnose degradation of various components of the gaseous fuel system.Further still, the control methods may provide for venting excessgaseous fuel from the gaseous fuel system prior to engine shutdown.

Turning now to FIG. 5, a high-level control method 500 for operating avehicle having a multi-fuel capable engine, such as a locomotive orother rail vehicle, is illustrated. Method 500 may be carried outaccording to instructions stored on a control system, such as controller136. At 502, method 500 includes determining operating parameters. Thedetermined operating parameters may include, but are not limited to,desired vehicle operating state (e.g., self-load or propulsion,explained in more detail below), notch throttle setting, liquid andgaseous fuel tank storage levels, vehicle and/or tender maintenancestatus (e.g., if one or more of the vehicle or fuel tender has recentlyundergone is currently undergoing maintenance), engine on/off requests,engine speed, engine temperature, etc.

At 504, if indicated by the operating conditions, the engine operates inliquid fuel only or in multi-fuel mode, as explained in more detailbelow with respect to FIG. 6. Briefly, engine operation in a liquid fuelonly mode or in a multi-fuel mode may include combusting liquid and/orgaseous fuel in the engine according to a predetermined substitutionratio in order to provide commanded engine output (which may bedetermined based on the commanded notch throttle setting, for example).The engine output may be transferred to one or more tractive motors viaa power conversion unit during a propulsion mode, or the engine outputmay be transferred to set of resistors via the power conversion unit anddissipated as heat during a self-load mode.

At 506, it is determined if a gaseous fuel system performance test isindicated. The gaseous fuel system performance test may be performed thefirst time a fuel tender is brought into operation, or it may beperformed after maintenance has performed on the fuel tender and/or railvehicle. Thus, determining if the gaseous fuel performance test isindicated may include determining the operational age of the fuel tenderand/or other components of the gaseous fuel system (based on input froman operator of the locomotive, for example), determining if maintenancewas recently performed on the fuel tender and/or other components of thegaseous fuel system, or other parameters. The gaseous fuel systemperformance test may include determining if the gaseous fuel system issufficiently able to deliver requested gaseous fuel to the locomotive orother vehicle engine over a range of engine operating points while thelocomotive operates in a self-load mode. Thus, the gaseous fuel systemperformance test may be performed before the locomotive or other vehicleoperates in a propulsion mode. If the gaseous fuel system performancetest is indicated, method 500 proceeds to 508 to perform the gaseousfuel system performance test, which will be described in more detailbelow with respect to FIG. 7.

If the gaseous fuel system performance test is not indicated, or uponcompletion of the gaseous fuel system performance test, method 500proceeds to 510 to determine if a gaseous fuel system leak test isindicated. The gaseous fuel system leak test may be performed todetermine if a leak is present in one or more components of the gaseousfuel system. For example, the leak test may indicate the presence of aleak in the fuel supply line, one or more of the gas admission valves,or the gaseous fuel passage coupled to the gas admission valves.Further, in some examples, the gaseous fuel system leak test mayindicate the presence of a leak in the fuel supply line and/or gaseousfuel storage tank on board the fuel tender.

In a first example, the gaseous fuel system leak test may be performedafter a predetermined amount of time has elapsed since a previous leaktest was performed, for example after one week or one month, or after apredetermined travel distance, such as 100 km. In a second example, thegaseous fuel system leak test may be performed when a set of operatingconditions is met (e.g., when the engine switches from multi-fuel modeto liquid-only mode, when the locomotive or other vehicle operates inthe self-load mode). In a third example, the gaseous fuel system leaktest may be performed upon an indication that a leak may be present inthe fuel system, such as if actual engine output is less than commandedengine output. The gaseous fuel system leak test may be performedimmediately after the gaseous fuel system performance test is performedin some examples, or it may be performed immediately after thedetermination that the gaseous fuel system performance test is notindicated. In other examples, the gaseous fuel system leak test may beperformed after an amount of time has elapsed following performance ofthe system performance test or following the determination that theperformance test is not indicated. As such, method 500 may includecontinuing to operate the engine in liquid-only or multi-fuel modeaccording to operating parameters, in order to provide desired engineoutput, prior to performing the gaseous fuel system leak test.

If performance of the gaseous fuel system leak test is indicated, method500 proceeds to 512 to perform the gaseous fuel system leak test, whichwill be described in more detail below with respect to FIG. 8. If theleak test is not indicated, or upon completion of the leak test, method500 proceeds to 514 to determine if an engine shutdown request isreceived. The engine shutdown request may be received in response to anoperator input, in response to a predetermined trip planner indicatingthe current trip has ended, or in response to an emergency stop requestreceived based on indicated engine, locomotive, and/or fuel tenderdegradation, for example.

If an engine shutdown request is not received, method 500 proceeds to518 to continue to operate the engine in liquid fuel only or multi-fuelmode, according to operating conditions (such as those explained belowwith respect to FIG. 6). Method 500 then returns to 510 to continue toassess if a leak test is indicated and if an engine shutdown request isreceived. If an engine shutdown request is received, method 500 proceedsto 516 to vent gaseous fuel prior to shutting the engine down, whichwill be explained in more detail below with respect to FIG. 9. Aftershutting down the engine, method 500 ends.

FIG. 6 is a method 600 for operating a multi-fuel capable engine. Method600 may be carried out according to instructions stored on a controlsystem, such as controller 136, in order to operate an engine witheither liquid fuel only combustion or with liquid fuel and gaseous fuelcombustion. Further, method 600 may be carried out in order to operatethe engine in either a self-load mode where engine output is dissipatedas heat or to operate the engine in a propulsion mode where engineoutput is used to propel the vehicle (e.g., locomotive) in which theengine is installed, such as via one or more tractive motors. Method 600may be executed during a portion or an entirety of method 500 of FIG. 5.

At 602, method 600 includes determining if self-load operation isindicated. As explained above, self-load operation includes at least aportion of the engine output produced from combustion being dissipatedas heat rather than being used to propel the vehicle in which the engineinstalled. Self-load operation may be carried out during maintenance ofthe locomotive or other vehicle or fuel tender (e.g., in order to allowoperation of various engine and/or vehicle components without movementof the vehicle), during one or more diagnostic routines (such as whenthe gaseous fuel system performance test or leak test is carried out),and/or during an extended idle operation. Thus, self-load operation maybe indicated based on a request from an operator, based on a commandeddiagnostic routine being performed, and/or based on a set of operatingparameters being met (such as notch throttle at idle with battery and/orcapacitance state of charge above a threshold).

If self-load operation is indicated, method 600 proceeds to 610, whichwill be explained in more detail below. If self-load operation is notindicated, method 600 proceeds to 604 to set the fuel substitution ratiobased on operating parameters. Engines configured to operate with bothliquid and gaseous fuel may be operated with as much gaseous fuel aspossible while still maintaining requested engine power. For example, instandard liquid-fueled engines, such as diesel engines, 100% of producedengine power may be derived from combustion of diesel fuel. Inmulti-fuel engines, a portion of the engine power may be derived fromgaseous fuel while the remaining engine power may be derived from liquidfuel. For example, as much as 80% of produced engine power may bederived from combustion of gaseous fuel, with the remaining 20% of powerderived from the combustion of diesel fuel. The amount of gaseous fuel“substituted” for the liquid fuel may be referred to as a substitutionratio. The substitution ratio may reflect the portion of engine powerderived from gaseous fuel. For example, a substitution ratio of 80indicates 80% of the power is derived from gaseous fuel, while asubstitution ratio of 50 indicates 50% of the power is derived fromgaseous fuel. A substitution ratio of 0 indicates liquid-only operation.

The substitution ratio may be set based on engine temperature, desiredfuel type, notch throttle position, relative fuel levels in each fueltank (e.g., if the level of gaseous fuel is below a threshold, moreliquid fuel may be used), vehicle location (e.g., whether the vehicle isin a tunnel), and/or other parameters. At 606, the gaseous and/or liquidfuel is supplied to each cylinder of the engine at the set substitutionratio. In some examples, the set substitution ratio may be the same forall cylinders. In other examples, one or more cylinders may havedifferent substitution ratios.

If the substitution ratio is greater than zero (e.g., if at least somegaseous fuel is supplied), the gaseous fuel may be premixed with intakeair and combusted due to compression ignition of the injected liquidfuel. The liquid fuel may be injected at a prescribed time during thecombustion cycle (such as the end of the compression stroke or beginningof the power stroke) such that the liquid fuel ignites quickly afterinjection due to increased cylinder temperature at high compressionlevels. The ignited liquid fuel may then ignite the premixed gaseousfuel and air. At 608, power produced by the combustion in the engine istransferred to a plurality of tractive motors via the power conversionunit to propel the vehicle.

Returning to 602, if is determined that self-load operation isindicated, method 600 proceeds to 610 to receive a request to operate ineither liquid fuel only mode or in multi-fuel mode. In some examples,the request may be sent responsive to input from an operator. Forexample, during the self-load operation, the fuel tender may beundergoing maintenance. As such, the operator may request operation withliquid fuel only combustion to avoid the transmission of gaseous fuelduring the maintenance procedure. In another example, the operator mayrequest multi-fuel operation when the fuel tender is undergoingmaintenance in order to allow various components of the fuel tender tobe assessed while the fuel tender is supplying gaseous fuel to thelocomotive. In further examples, operation in liquid fuel only or inmulti-fuel mode may be determined automatically by the controller basedon operating parameters, as explained above. In still further examples,the engine may be operated in multi-fuel mode during self-load operationwhen the gaseous fuel system performance test is being performed,explained in more detail below.

At 612, method 600 includes setting the fuel substitution ratio based onoperating parameters. When the engine is operated with multi-fuelcombustion during the self-load mode, the substitution ratio may be setbased on the same factors as during the propulsion mode, such as basedon the notch throttle setting. At 614, the power output from the engineis transferred to the power conversion unit and dissipated via the setof resistors.

Thus, method 600 of FIG. 6 provides for operating a vehicle, such as alocomotive, in either a self-load mode or in a propulsion mode. Duringthe self-load mode, the engine may be operated with either liquid fuelonly combustion (e.g., the engine may combust only diesel fuel) or withmulti-fuel combustion (e.g., the engine may combust both diesel andnatural gas). When operating in the self-load mode, the decision tocombust either only liquid fuel or both liquid and gaseous fuel may bemade automatically based on operating conditions (e.g., if a gaseousfuel system performance test is being performed, the engine will beoperated with multi-fuel combustion). However, in some conditions theoperator of the vehicle may choose if the engine operates with onlyliquid fuel combustion or if the engine operates with multi-fuelcombustion, based on the maintenance state of the locomotive or fueltender, for example.

Turning to FIG. 7, a method 700 for performing a gaseous fuel systemperformance test is presented. Method 700 may be carried out by acontrol system, such as controller, according to instructions storedthereon. As explained above with respect to FIG. 5, the gaseous fuelsystem performance test may be carried out prior to the fuel tenderbeing put into operation, for example following manufacture of the fueltender or following maintenance of the fuel tender. Additionally, asexplained above with respect to FIG. 6, the gaseous fuel systemperformance test may be carried out during a self-load operation, suchas the self-load operation described above with respect to FIG. 6.

At 702, method 700 includes delivering liquid and gaseous fuel to theengine at a specified substitution ratio and notch throttle setting. Thespecified substitution ratio and notch throttle setting may be based onthe progression of the performance test. For example, the gaseous fuelsystem performance test may include a series of engine operating points,including a series of substitution ratios and notch throttle settings,that the engine is operated under to determine that the fuel tender isdelivering gaseous fuel to the locomotive at amounts and/or ratesrequested by the locomotive controller. Thus, when the performance testis initially started, the engine may be operated with a first specifiedsubstitution ratio and a first specified notch throttle setting. Then,as the performance test progresses, the substitution ratio may beincrementally adjusted such that the engine is operated over a range ofsubstitution ratios, such as from a minimum substitution ratio (e.g.,zero) to a maximum substitution ratio (e.g., 80). Likewise, as theperformance test progresses, the notch throttle setting may beincrementally adjusted such that the engine is operated over a range ofnotch throttle settings, such as from a minimum notch setting (e.g.,idle) to a maximum substitution ratio (e.g., notch 8).

As used herein, a minimum engine operating point, such as minimum notchthrottle setting, comprises the lowest operating point possible, with nolower operating points below it. Thus, the minimum notch throttlesetting may be idle or dynamic braking, and the minimum substitutionratio may be zero (e.g., no gaseous fuel). The maximum engine operatingpoint comprises the highest operating point possible, with no higheroperating points above it. Thus, the maximum notch throttle setting maybe notch eight for a standard notch-eight throttle, although higher orlower notch settings are possible. The maximum substitution ratio may be100 in some examples (with no liquid fuel delivered), or may be a ratiolower than 100 (for example, it may be the ratio with the highest amountof gaseous fuel possible that still maintains combustion).

In some examples, the specified engine operating points over which theengine is operated during the performance test may include operatingpoints predicted to be encountered during a subsequent engine operatingperiod (where the engine is operating to propel the vehicle in which itis installed, for example). In some examples, the predicted engineoperating points may include the full range of operating pointsdescribed above. In other examples, the predicted engine operatingpoints may include only a subset of the full range of operating points.In one example, a trip plan may be determined for the subsequent engineoperation that includes predicted location, vehicle speed, grade,traction, notch throttle setting, etc., for each segment of thesubsequent engine operation. Based on the trip plan, the specifiedoperating points may be determined, and during the performance test, theengine may be operated at each of the specified operating points.

After the liquid and/or gaseous fuel is delivered to the engine at thespecified substitution ratio and specified notch throttle setting, thepower from the engine is transferred to the power conversion unit anddissipated via the set of resistors at 704. At 706, the engine fuelsystem parameters are monitored. The monitored parameters may includeengine output, gaseous fuel supply pressure, engine temperature, and/orother engine or fuel system parameters. The engine output may bemonitored by monitoring one or more of engine speed (based on feedbackfrom an engine speed sensor, for example), engine temperature (based onfeedback from a temperature sensor positioned to determine enginecoolant temperature, for example, or based on feedback from an exhausttemperature sensor), exhaust pressure (based on feedback from an exhaustpressure sensor, for example), and load on the power conversion unit.

At 708, method 700 includes determining if the measured parameters aredifferent than expected. In an example where engine output is monitored,the measured engine output may be determined to be different than theexpected engine output if the measured engine output differs from theexpected engine output by more than a threshold, such as by more than5%. If the measured parameters are different than expected, method 700proceeds to 710 to indicate degradation of the gaseous fuel system andtake default action. Indicating degradation may include outputting anotification to an operator of the locomotive that the gaseous fuelsystem may be degraded, as indicated at 711. The default action mayinclude notifying an operator to have maintenance performed on the fueltender or other components of the gaseous fuel system (e.g., gasadmission valves) before putting the gaseous fuel system into operationand/or setting a diagnostic code. If degradation of the gaseous fuelsystem is indicated, the engine may be operated with liquid fuel onlycombustion and without gaseous fuel combustion, and/or the engine may beshutdown.

If the engine output is not different than expected, method 700 proceedsto 712 to determine if the engine has been operated with all thespecified substitution ratios and notch throttle settings. For example,as explained above, the engine may be operated over a range ofsubstitution ratios, starting at zero and progressing to a maximumallowable substitution ratio. For example, the engine may be operated atthe substitution ratios of 0, 10, 20, 30, 40, 50, 60, 70, and 80, withengine output monitored and compared to expected output at eachsubstitution ratio. Similarly, the engine may be operated over a rangeof notch throttle settings, for example the engine may be operated ateach notch throttle setting, with the expected engine output compared tothe measured engine output after operation at each notch throttlesetting. Further, the engine may be operated over a range substitutionratios and notch throttle setting combinations, such as operated at morethan one substitution ratio per notch throttle setting. Other engineoperating points during the gaseous fuel system performance test arepossible. It is to be understood that while some notch throttle settingsmay be capable of being operated at with more than one substitutionratio, other notch throttle settings may have only one substitutionratio at which the engine can be operated. For example, when the notchthrottle is set to zero or to notch 8, it may only be possible tooperate the engine with liquid fuel only combustion, and thus only onesubstitution ratio (zero) may be possible.

If method 700 determines that the engine has been operated at all theoperating points (e.g., substitution ratios and notch throttle settings)specified by the gaseous fuel system performance test, method 700proceeds to 714 to indicate that no degradation of the gaseous fuelsystem is present, and an operator is notified of the test results at715. If it is determined that not all of the specified engine operatingpoints have been reached, method 700 proceeds to 716 to adjust thesubstitution ratio and/or notch throttle setting to the next specifiedsubstitution ratio and/or notch throttle setting, and then method 700returns to 702 to repeat the fuel delivery, power transfer, andmonitoring of the engine output.

Thus, method 700 of FIG. 7 provides for testing the performance of thegaseous fuel system after maintenance or during initial operation of thegaseous fuel system. The test includes operating the locomotive in aself-load and multi-fuel mode. The test also includes incrementingthrough various engine operating points, from 0-max substitution ratio,idle to notch 8 notch throttle setting, into and out of multi-fuel mode,etc., to hit performance boundaries. The engine output is monitored(e.g., based on exhaust temperature, exhaust pressure, and/or alternatorload, for example) to determine if actual output matches the expectedoutput for the commanded notch setting. During execution of theperformance test, information may be displayed to an operator of thelocomotive on a display of the locomotive, for example, to allow theoperator to see how the gaseous fuel system is performing during thetest. The displayed information may include information received fromthe fuel tender, such as gaseous fuel pressure in the fuel tender,gaseous fuel flow rate, instructions received from the locomotivecontroller, etc.

FIG. 8 illustrates a method 800 for performing a gaseous fuel systemleak test. Method 800 may be carried by a control system, such ascontroller, according to instructions stored thereon, in order todetermine if a leak is present in the gaseous fuel system. As explainedabove with respect to FIG. 5, the leak test may be performed whenindicated by a specified elapsed amount of time or travel distance sincea previous test was performed, and/or based on a set of operatingconditions being met. The leak test may be performed during a self-loadmode or during a propulsion mode.

At 802, method 800 includes sending a request to the gaseous fuel systemto deliver gaseous fuel to the engine. The request may include sending arequest to the fuel tender (e.g., by sending the request to the fueltender controller) to vaporize stored liquefied fuel into gaseous fueland send the gaseous fuel to the locomotive. The request may alsoinclude adjusting a pressure regulator and/or one or more gaseous fuelcontrol valves to increase the pressure in the gaseous fuel supply lineto a threshold pressure.

At 804, method 800 includes sending a request to close one or moregaseous fuel valves in the gaseous fuel system. The gaseous fuel valvesclosed in response to the request may include a fuel valve coupledbetween the vaporizer and the locomotive (e.g., valve 232), one or moregaseous fuel valves positioned in the gaseous fuel supply line on thelocomotive (e.g., valves 442, 444, and/or 446), and/or one or more gasadmission valves. At 806, method 800 includes operating the engine withliquid fuel only combustion. Operation with liquid fuel only combustionmay include sending a request to the fuel tender to stop sending gaseousfuel to the locomotive. By initially supplying gaseous fuel to theengine, and then closing one or more gaseous fuel valves, the gaseousfuel system may be segmented into portions that can be monitored forexpected changes in fuel pressure as the pressure in the fuel supplyline decays following the closure of the valves and/or cessation of thegaseous fuel supply, e.g., gaseous fuel may slowly leak past the gasadmission valves into the engine.

At 808, the pressure drop across each closed gaseous fuel valve ismonitored, and compared to an expected pressure drop. The pressure dropmay be monitored based on output from one or more pressure sensors inthe gaseous fuel supply line, for example. The output from one or moreof the pressure sensors may be received via the fuel tender controllerin some examples. At 810, it is determined if any of the monitoredpressure drops is different than a respective expected pressure. Forexample, the pressure may be expected to decrease at a certainpredetermined rate (based on the initial fuel line pressure and knownleakage rate of the gas admission valves, for example). A pressure dropdifferent than expected may include the monitored pressure decreasingfaster than the predetermined rate, e.g., by more than a thresholdamount, such decreasing at a rate 5% or 10% faster than expected. Ifnone of the monitored pressures is different than expected, method 800proceeds to 812 to indicate that no leaks are present in the gaseousfuel system and output a notification that no leaks are present fordisplay to an operator. If any one of the monitored pressures isdifferent than the respective expected pressure, method 800 proceeds to814 to indicate a gaseous fuel system leak is detected and anotification of the leak is output to an operator. The notification mayinclude an indication of which segment of the gaseous fuel systemincludes the leak. Further, in some examples, when a gaseous fuel systemleak is detected, multi-fuel operation may be stopped until the leak isrepaired (e.g., the gaseous fuel supply may be disabled and the engineoperated with liquid fuel only combustion, of the engine may be shutdown).

Thus, method 800 of FIG. 8 detects fuel leaks in a gaseous fuel system.The method includes sending a request to the fuel tender to send gaseousfuel to the engine on board the locomotive. One or more gaseous fuelvalves are closed to segment the gaseous fuel system into sections andeach section is monitored for a drop in fuel pressure. Fast pressuredrops indicate a leak in the gaseous fuel system. The monitored sectionsmay include from the LNG storage tank to the vaporizer, the vaporizer tolocomotive, and the locomotive to engine (via the gas admission valves).Thus, the method also includes sending a request to close one or moregaseous fuel valves, receiving information indicative of pressure in thegaseous fuel line supply line (both on board the locomotive and on boardthe fuel tender), and if the pressure is different than expected,indicating leak is present and taking default action. The default actionmay include stopping multi-fuel operation.

FIG. 9 illustrates a method 900 for venting excess fuel from a gaseousfuel system prior to shutdown of the engine. Method 900 may be carriedout according to instructions stored on a control system, such ascontroller, in response to a request to shut down the engine, such asthe engine shutdown request explained above with respect to FIG. 5. Insome examples, method 900 may be performed when switching from operationin multi-fuel mode to operation in liquid-fuel only mode. The gaseousfuel is vented through the engine, where it does not undergo combustionbut is instead routed through the engine exhaust system, which in someexamples includes one or more exhaust emission control devices toconvert the unburned gaseous fuel rather than releasing it toatmosphere.

At 902, method 900 includes sending a request to a gaseous fuel systemto stop delivering gaseous fuel to the engine. The request may be sentto a controller on board the fuel tender, and in response the vaporizerand/or gaseous fuel pump may be deactivated and/or one or more fuelvalves on the fuel tender may be closed. At 904, the engine is operatedat idle with liquid fuel only combustion. At 906, the gas admissionvalves of the engine are opened. Further, a request may be sent to openother valves in the gaseous fuel supply line and/or on the fuel tender,such as valve 232 and/or valves 442 and 446. In doing so, the gaseousfuel remaining in the gaseous fuel supply line may be drawn into theengine due to the vacuum created by operating the engine at idle. Thegaseous may not be combusted in the cylinders, however, due to therelatively low amount of gaseous fuel in each cylinder. Rather, thegaseous fuel is routed through the engine to the engine exhaust system.

In some embodiments, the locomotive may include a purge line fluidicallycoupled to the gaseous fuel supply line. Gas, such as ambient air, freshair, inert gas, etc., may be routed through the gaseous fuel supply linevia the purge line to purge any remaining gaseous fuel out of the supplyline. To optimize flow of purge gas through the gaseous fuel supplyline, a bypass passage around the pressure regulator may be provided.Thus, method 900 may optionally include at 908 sending a request to openone or more additional gaseous fuel valves, such as valve 444 in thebypass passage coupled across the pressure regulator, and at 910,opening an admission valve in a purge line, such as valve 442, to purgegas through the fuel supply line.

At 912, method 900 determines if gaseous fuel in the gaseous fuel supplyline is below a threshold. The threshold may be a suitable thresholdamount of gaseous fuel, such as any detectable gaseous fuel. Whether thegaseous fuel in the gaseous fuel supply line is below the threshold maybe determined based on a sensor that detects the amount and/or flow rateof the gaseous fuel in the supply line, or based on a predeterminedduration of the gaseous fuel venting. If it is determined that thegaseous fuel is not below the threshold, method 900 proceeds to 914 tocontinue to operate at idle with the gas admission valves open and thenmethod 900 loops back to 912. If it is determined that the amount ofgaseous fuel has dropped below the threshold, method 900 proceeds to 916to take default action, such as shutting down the engine or operating inliquid-fuel only mode, and method 900 ends.

Thus, method 900 of FIG. 9 provides for venting excess gaseous fuel toan engine exhaust system. Upon indication that the locomotive is aboutto shutdown, the notch throttle is set to idle to cause intake manifoldvacuum. The valves in the gaseous fuel system are opened to supplygaseous fuel in supply line to the engine (while not supplying new fuelfrom the gaseous fuel tank). In this way, the engine will suck gaseousfuel out of the supply line to the cylinders (but with the substitutionratio too low to combust the gaseous fuel, it will just travel throughcylinders and out the exhaust). The method may further supply fresh airto the gaseous supply line to further purge the fuel. In some examples,instead of building vacuum with idle engine operation, the air purgeline could be pressurized with pressurized air to purge the gaseous fuelto the engine. Purge of the gaseous fuel may occur for a predeterminedamount of time and/or until a gaseous fuel detection unit near theengine indicates that there is no gaseous fuel left in supply line.

Method 900 illustrates a venting routine that may be carried out duringstandard engine shutdown. However, during certain conditions, such as ifdegradation of a turbocharger or other vehicle or engine component isdetected, the engine may be immediately shutdown to prevent catastrophicdamage to the engine or vehicle. Such a shutdown may be referred to asan emergency shutdown. During an emergency shutdown, operation at idleto vent the gaseous fuel to the engine may not be desired. Accordingly,a vent valve in a passage fluidically coupling the gaseous fuel supplyline to atmosphere may be opened, such as valve 448, to quickly purgethe gaseous fuel to atmosphere.

Additionally, in some embodiments when the engine is run at idle tocreate vacuum in intake manifold and draw in ambient air at the far endof fuel supply line and consume the remaining gaseous fuel in the supplyline, gases other ambient air may be drawn in, such as generic versions,e.g., inert, atmospheric, etc. Further, when an intake manifold pressureis present (e.g., no intake vacuum), the engine may be operated at otherengine load levels which will require a pressurized gas source on or offthe locomotive in order to overcome the intake manifold pressure. Thiscould include ambient air or a specific type of gas like “inert gas,”etc. Further still, when the engine is turned off before the gaseousfuel is vented to the engine, the gaseous fuel could bypass the engineand be vent to atmosphere or to a recapture vessel.

Thus, the systems and methods described herein provide for monitoringthe health of a vehicle, such as a locomotive, in conjunction with thehealth of a gaseous fuel supply. In some examples, the gaseous fuelsupply may be at least partially included on fuel tender remote from thelocomotive. Accordingly, the locomotive and fuel tender may be monitoredas an integrated system to detect a system issue such as degradation offuel tender performance or a gaseous fuel system leak, and report theissue to an operator of the locomotive.

In an embodiment, a system comprises a liquid fuel system to deliverliquid fuel to an engine; a gaseous fuel system to deliver gaseous fuelto the engine; and a control system configured to: during a gaseous fuelsystem test mode, control the liquid fuel system and the gaseous fuelsystem to deliver the liquid fuel and the gaseous fuel to the engineover a range of engine operating points; and indicate degradation of thegaseous fuel system based on engine output at each of the engineoperating points. In an example, the degradation may be indicated by thecontrol system outputting a notification for display to an operator.

The system may further comprise a power conversion unit coupled to theengine and a power dissipater unit (e.g., set of resistors) coupled tothe power conversion unit and configured to dissipate power from thepower conversion unit as heat, and wherein the control system isconfigured to, during the gaseous fuel system test mode, transfer powerfrom the engine to the power conversion unit and dissipate the power viapower dissipation unit.

In one example, the range of engine operating points may include eachnotch throttle setting predicted to be operated at during a subsequentengine operating period, from idle to a maximum notch throttle setting.In another example, the range of engine operating points includes arange of ratios of an amount of gaseous fuel relative to an amount ofliquid fuel predicted to be operated at during a subsequent engineoperating period, from a minimum ratio to a maximum ratio.

The control system may be configured to determine engine output based onone or more of exhaust temperature, exhaust pressure, or powerconversion unit load. The control system may also be configured to,during a self-load mode, operate the engine with either liquid fuel onlyor liquid and gaseous fuel based on operator input, and transfer powerfrom the engine to the power conversion unit and dissipate the power.The control system may be configured to, during a propulsion mode,operate engine with either liquid fuel only or liquid and gaseous fuelbased on engine operating conditions and transfer power from the engineto a plurality of tractive motors via the power conversion unit.

Another embodiment for a system comprises a liquid fuel system todeliver liquid fuel to an engine; a gaseous fuel system to delivergaseous fuel to the engine, the gaseous fuel system comprising: agaseous fuel supply fluidically coupled to the engine via a gaseous fuelsupply line; one or more gaseous fuel valves positioned in the gaseousfuel supply line; and one or more gas admission valves positionedbetween the gaseous fuel supply line and the engine; and a controlsystem configured to: responsive to a request to vent excess gaseousfuel in the gaseous fuel system, operate the engine at idle with liquidfuel-only combustion; send a request to stop sending fuel from thegaseous fuel supply to the engine; and send a request to open the one ormore gaseous fuel valves and the one or more gas admission valves.

The gaseous fuel supply may include a fuel tank and a vaporizer locatedremotely from the engine. The one or more gaseous fuel valves mayinclude a bypass valve coupled across a pressure regulator. The systemmay further comprise an air purge line coupled to the fuel supply line,and the control system may be configured to open an air purge lineadmission valve positioned in the air purge line responsive to therequest to vent the gaseous fuel. The control system may be configuredto maintain the one or more gaseous fuel valves and the one or more gasadmission valves open for a predetermined amount of time and/or until agaseous fuel detection unit positioned in the fuel supply line near theengine indicates an amount of gaseous fuel in the supply line hasdropped below a threshold amount. The control system may be configuredto, after the predetermined amount of time is reached and/or after theamount of gaseous fuel in the supply line has dropped below thethreshold amount, shutdown the engine or operate in a liquid fuel-onlymode.

A further embodiment for a system comprises a liquid fuel system todeliver liquid fuel to an engine; a gaseous fuel system to delivergaseous fuel to the engine; and a control system configured to: during agaseous fuel leak detection mode, send a request to the gaseous fuelsystem to deliver gaseous fuel to the engine; send a request to closeone or more gaseous fuel valves in the gaseous fuel system and operatethe engine with liquid fuel-only combustion; monitor a respectivepressure drop across each of the one or more closed gaseous fuel valves;and if a pressure drop across at least one of the closed gaseous fuelvalves is different than expected (e.g., exceeds a determined thresholdvalue), indicate a leak in the gaseous fuel system.

The one or more gaseous fuel valves may comprise a gaseous fuel valvepositioned in a gaseous fuel supply line between a fuel tank and avaporizer. In an example, the control system is configured to monitor apressure drop across the closed gaseous fuel valve by receivinginformation indicating a pressure upstream and a pressure downstream ofthe closed gaseous fuel valve. The one or more gaseous fuel valves maycomprise one or more gaseous fuel valves positioned in a gaseous fuelsupply line between a vaporizer and the engine. In one example, thecontrol system is configured to monitor a respective pressure dropacross each of the one or more closed gaseous fuel valves by receivinginformation indicating a respective pressure upstream and a respectivepressure downstream of each of the one or more closed gaseous fuelvalves. The control system may be configured to continue to operate theengine with liquid fuel-only combustion if a leak in the gaseous fuelsystem is indicated. The control system may be configured to, whenindicated by engine operating parameters, resume delivering gaseous fuelto the engine in order to operate the engine with multi-fuel combustionif a leak in the gaseous fuel system is not indicated.

An embodiment of a system comprises a liquid fuel system to deliverliquid fuel to an engine; a gaseous fuel system to deliver gaseous fuelto the engine; a power conversion unit coupled to the engine and a setof resistors coupled to the power conversion unit and configured todissipate power from the power conversion unit as heat; and a controlsystem configured to, during a self-load mode of operation of the enginewhere the power from the power conversion unit is dissipated as heat inthe set of resistors: operate the engine with the liquid fuel onlyresponsive to a first operator input; and operate the engine withmulti-fuel combustion of the liquid fuel and the gaseous fuel responsiveto a second operator input.

In an embodiment, a method for operating an engine adapted to operatewith liquid fuel and gaseous fuel comprises: delivering one or more ofliquid fuel and gaseous fuel to the engine for combustion in the engine;during a self-load mode of operation, transferring engine output to aset of resistors via a power conversion unit and dissipating the engineoutput as heat; during a propulsion mode of operation, transferringengine output to a plurality of tractive motors via the power conversionunit; during a gaseous fuel system performance test mode: operating theengine over a range of engine operating points; monitoring engine outputat each engine operating point; and indicating degradation of thegaseous fuel system based on engine output at each of the engineoperating points; during a gaseous fuel system leak test mode: sending arequest to receive gaseous fuel; closing one more gaseous fuel valves;operating with liquid fuel only combustion; monitoring a pressure dropacross each closed gaseous fuel valve; and indicating a leak in thegaseous fuel system if at least one of the monitored pressure drops isdifferent than expected; and during a gaseous fuel venting modeperformed responsive to a request to shut down the engine: operating theengine at idle; sending a request to stop sending gaseous fuel to theengine; and sending a request to open one or more gaseous fuel valves.

An embodiment relates to a method for operating an engine adapted tooperate with liquid fuel and gaseous fuel. The method comprisesreceiving a request to operate in a self-load mode. The method includes,responsive to receiving the request, selecting a first fuel substitutionratio, delivering one or more of gaseous fuel and liquid fuel to theengine at the first fuel substitution ratio, and transferring engineoutput to a set of resistors via a power conversion unit and dissipatingthe engine output as heat. The method includes selecting a second fuelsubstitution ratio, delivering one or more of the gaseous fuel andliquid fuel to the engine at the second fuel substitution ratio, andtransferring engine output to the set of resistors via the powerconversion unit.

In an example, selecting a first fuel substitution ratio comprisesreceiving a request from an operator to operate the engine in amulti-fuel mode and selecting the first fuel substitution ratio based onengine operating parameters. The selected first fuel substitution ratiomay be greater than zero such that at least some gaseous fuel isdelivered to the engine. Selecting the second fuel substitution ratiocomprises receiving a request from the operator to operate the engine ina liquid fuel only mode and delivering only liquid fuel to the enginewithout delivering gaseous fuel to the engine.

In another example, selecting a first fuel substation ratio comprisesreceiving a request to perform a gaseous fuel system performance testand selecting a first fuel substitution ratio specified by the gaseousfuel system performance test. Selecting the second fuel substitutionratio comprises selecting a next fuel substitution ratio specified bythe gaseous fuel system performance test.

A method for operating an engine adapted to operate with liquid fuel andgaseous fuel is provided. In one example, the method includes receivinga first request to vent gaseous fuel from a gaseous fuel system,operating the engine at idle responsive to the first request, sending asecond request to stop sending gaseous fuel to the engine, and sending athird request to open one or more gaseous fuel valves. Responsive to apredetermined amount of time elapsing, the method includes shutting downthe engine. The method also includes following the shutting down of theengine, receiving a fourth request to restart the engine, the fourthrequest further including a request to perform a gaseous fuel systemperformance test. Responsive to receiving the fourth request, the methodincludes operating the engine over a range of engine operating points,monitoring engine output at each engine operating point, and indicatingdegradation of the gaseous fuel system based on engine output at each ofthe engine operating points. The method may also include, during theoperation of the engine over the range of operating points, transferringengine output to a set of resistors via a power conversion unit anddissipating the engine output as heat.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty. The terms “including” and “in which” are used as theplain-language equivalents of the respective terms “comprising” and“wherein.” Moreover, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

The invention claimed is:
 1. A system, comprising: a liquid fuel systemto deliver liquid fuel to an engine; a gaseous fuel system to delivergaseous fuel to the engine; and a control system configured to: during agaseous fuel system test mode, control the liquid fuel system and thegaseous fuel system to deliver the liquid fuel and the gaseous fuel,respectively, to the engine over a range of engine operating pointsincluding each notch throttle setting and a range of ratios of an amountof gaseous fuel relative to an amount of liquid fuel; and indicatedegradation of the gaseous fuel system based on engine output at each ofthe engine operating points.
 2. The system of claim 1, wherein eachnotch throttle setting is predicted to be operated at during asubsequent engine operating period, from a minimum to a maximum notchthrottle setting.
 3. The system of claim 1, wherein the range of ratiosof the amount of gaseous fuel relative to the amount of liquid fuel ispredicted to be operated during a subsequent engine operating period,from a minimum ratio to a maximum ratio.
 4. The system of claim 1,wherein the control system is configured to determine the engine outputbased on one or more of exhaust temperature, exhaust pressure, or powerconversion unit load.
 5. The system of claim 1, further comprising apower conversion unit coupled to the engine and a power dissipater unitcoupled to the power conversion unit, and the control system isconfigured to, during the gaseous fuel system test mode, transfer powerfrom the engine to the power conversion unit and thereby to dissipatethe power.
 6. The system of claim 5, wherein the control system isconfigured to, during a self-load mode, operate the engine with eitherthe liquid fuel only or the liquid fuel and the gaseous fuel based onoperator input, and transfer power from the engine to the powerconversion unit and dissipate the power.
 7. The system of claim 5,wherein the control system is configured to, during a propulsion mode,operate the engine with either the liquid fuel only or the liquid fueland the gaseous fuel based on engine operating conditions and transferpower from the engine to a plurality of tractive motors via the powerconversion unit.
 8. The system of claim 1, wherein the control system isconfigured to indicate the degradation by outputting a notification fordisplay to an operator.
 9. The system of claim 1, wherein the liquidfuel is diesel and the gaseous fuel is natural gas.
 10. The system ofclaim 9, wherein the engine, the liquid fuel system, the gaseous fuelsystem, and the control system are at least partially onboard alocomotive.
 11. A system, comprising: a liquid fuel system to deliverliquid fuel to an engine; a gaseous fuel system to deliver gaseous fuelto the engine; and a control system configured to: during a gaseous fuelsystem test mode, deliver liquid and gaseous fuel to the engine over arange of specified substitution ratios and notch throttle settings;monitor an engine output at each specified substitution ratio and notchthrottle setting; and if the engine output differs from an expectedengine output by more than a threshold, indicate degradation of thegaseous fuel system.
 12. The system of claim 11, wherein the controlsystem is configured to indicate the degradation of the gaseous fuelsystem by outputting a notification for display to an operator.
 13. Thesystem of claim 11, wherein the range of specified substitution ratiosincludes ratios predicted to be operated during a subsequent engineoperating period, from a minimum to a maximum ratio.
 14. The system ofclaim 13, wherein the range of notch throttle settings includes eachnotch throttle setting predicted to be operated during a subsequentengine operating period, from a minimum to a maximum notch throttlesetting.
 15. The system of claim 14, wherein the minimum ratio is zeroand the minimum notch throttle setting is idle or dynamic braking. 16.The system of claim 11, wherein the engine output includes one or moreof exhaust temperature, exhaust pressure, or power conversion unit load.17. The system of claim 11, wherein the liquid fuel is diesel and thegaseous fuel is natural gas.
 18. The system of claim 17, wherein theengine, the liquid fuel system, the gaseous fuel system, and the controlsystem are at least partially onboard a locomotive.
 19. A system,comprising: a liquid fuel system to deliver liquid fuel to an engine; agaseous fuel system to deliver gaseous fuel to the engine; a powerconversion unit coupled to the engine and a set of resistors coupled tothe power conversion unit and configured to dissipate power from thepower conversion unit as heat; and a control system configured to,during a gaseous fuel system test mode: deliver the liquid fuel and thegaseous fuel, respectively, to the engine over a range of engineoperating points including each notch throttle setting and a range ofratios of an amount of gaseous fuel relative to an amount of liquidfuel; transfer power from the engine to the power conversion unit anddissipate the power via the set of resistors; indicate degradation ofthe gaseous fuel system based on engine output at each of the engineoperating points.
 20. The system of claim 19, wherein the liquid fuel isdiesel, the gaseous fuel is natural gas, and the engine, the liquid fuelsystem, the gaseous fuel system, and the control system are at leastpartially onboard a locomotive.